The present invention refers to a watertight compartment in a floating plant for processing crude oil and/or gas having at least one remotely releasable two-part connection piece for a riser between the sea floor and the plant.
For the processing of crude oil and/or gas from offshore wells a floating plant will be connected to one or more wells by a bundle of rigid pipes or flexible, reinforced hoses designed to withstand high pressures.
The pipes, or hoses, are usually connected to the plant by remotely releasable two-part connection pieces located outside the shell of the vessel carrying the plant, either above or below the water line. The releasability is necessary for rapidly moving the plant from the production site, for instance when dangerous icebergs appear. It will also be necessary to release the connection pieces if the anchoring devices or the automatic positioning system of the plant fails.
Connection pieces located above the water line will easily be damaged through collision with other vessels, or ice floes.
Connection pieces located below the water line can be located so they run considerably less risk of being damaged, for instance when mounted in the bottom plating of the vessel carrying the plant. With conventional vessels for this purpose the bottom plating will be located 15-20 meters below the water line. It will however then be necessary to use divers, or some diving equipment for inspection and overhaul of the connection pieces, which implies certain risks and is expensive.
One possible solution to simplify the work of inspection and overhaul of the rather complicated mechanism of a remotely releasable riser pipe connection piece is to locate the latter in a compartment, open downwards to the surrounding water, which is connected to a compressor for holding an air pressure within the compartment corresponding to the external water pressure. In such a manner the level of the water within the compartment can be maintained about at the downwardly directed opening.
This solution does, however, involve certain problems, in that the bulkheads surrounding the compartment must be dimensioned to withstand a rather high pressure, and that operating staff can remain within the compartment during a limited time only, without being subjected to time consuming decompression afterwards.